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Earth is itself sophisticated !

  1. Aug 26, 2011 #1
    Hiii , I have 3 questions .

    1. How can we move in opposite direction of Earth's rotation despite of earth's high velocity ?
    Image1 :http://tinypic.com/view.php?pic=a2wyh3&s=7

    2. Suppose we jump on the surface of earth , while earth is in rotation , then why we don't move backward or why we are not backward of the actual position in which we were standing before ?
    Image2 :http://tinypic.com/view.php?pic=119pb1d&s=7

    3. Do these same reasons of above two questions apply in train also , while we are jumping in it or moving in its opposite direction ( In moving train ) ? If so or not so why ?

    Please don't go on the images . I made them in hurry .

    Thanks in advance .

    ( I am 14 years , class 10th )

    Umm , atmosphere moves with the earth ? Why ? Due to gravity ? If yes then please explain that in detail .
    Last edited: Aug 26, 2011
  2. jcsd
  3. Aug 26, 2011 #2


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    The answer is inertia. Objects in motion tend to stay in motion. A person standing on the Earth is already moving with the rotating Earth and just continues to do so when he jumps. Inertia is why you can throw a ball. The ball keeps moving in the same direction it was at the moment you let go of it. If it wasn't for inertia, the ball would just drop straight down to the ground the instant it left your hand.
  4. Aug 26, 2011 #3


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    Like Janus said, Inertia is one of the primary answers. Another is to realize that speed is relative. If you are in an Airplane, no one in the plane appears to be moving at all. However to me on the ground waving goodbye, everyone is moving at several hundred miles per hour. We USUALLY refer to motion with regards to the ground just to avoid confusion, but it is not necessary to use the frame of reference of the Earths surface. After all the astronauts that walked on the Moon were certainly not using the Earth's frame to gauge how fast they went in their lunar rover!
  5. Aug 26, 2011 #4
    I find it easiest to think of it in terms of vectors. When you're on a train, you have a velocity going forwards, which if you throw a ball, adds to this vector.

    And if you don't know how vectors work, don't worry, they're not as hard as some might make you think.
  6. Aug 27, 2011 #5
    This is not the answer to my question . I know about the law of inertia which is the measure of mass and yes its the tendency of body to remain in its original position unless an external force acts on it . (Newton's first law right.)

    This is the answer of how an organism can remain at rest or uniform motion inspite of earth high linear (rotational ) velocity ?

    My three questions were different . Please refer my post #1 again .

    Thanks .

  7. Aug 27, 2011 #6
    You've only mentioned the intuitive half of Newton's first law. The second part of it says that unless a force is applied, IT WILL STAY AT THE SAME VELOCITY.

    Which means, if I'm going forward, there needs to be a force to make me stop, not a force to keep me going (in reality there's both, but again, that's due to vector addition).
  8. Aug 27, 2011 #7
    I am not talking about Newton's first law that is why I just gave its skeleton . Answer my three question in post #1.
  9. Aug 27, 2011 #8
    1. The Earth has a high velocity, but the acceleration (a centripetal acceleration) is rather small. It is easy to overcome this force, in fact, it's usually ignored and the Earth's surface considered an inertial frame of reference (which is not the case => approximation).

    2. Because of Newton's first law, we are moving with the Earth. Say we're going at 10m/s because we're on the surface of the Earth (that number is waaaaaaaaay off, but it's an example). When we jump up, we have an additional velocity in the upward direction. But that doesn't affect the horizontal direction, so we're still "rotating with the Earth". Hence, we land in the same place if we jump exactly perpendicular, at 90 degrees.

    3. The same two things also apply in a train, in fact, the train is usually used as an example of how velocity is relative to frame of reference.
  10. Aug 28, 2011 #9


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    This is simple newtonian mechanics, why is it hard to grasp? Do you expect to fall backwards against the earth's rotation?
  11. Aug 28, 2011 #10
    Yes , I got it theoretically . Can any one explain it mathematically (Questions in post #1)? Just little maths .
  12. Aug 28, 2011 #11
    I'd advise you against trying to simply understand numbers involved, as that will lead to a plug and chug mentality...very dangerous for a physicist.

    I'll let someone LaTex up the maths for you, I'd need to go and actually find out how to use it. :P
  13. Aug 29, 2011 #12


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    There's not really a need to, as it would greatly overcomplicate things.
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